Complex Interactions Between Genome Components of Two ToLCNDV Isolates from India and Spain Determine Effective Infection in Tomato

Tomato leaf curl New Delhi virus (ToLCNDV) is a bipartite begomovirus whose infectivity and host range depend on the coordinated functions of its DNA-A and DNA-B components. Here, we investigated the replication, movement, and systemic infection capacity of ToLCNDV isolates from India (IN) and Spain (ES) and their pseudo-recombinants in tomato and Nicotiana benthamiana. In tomato, the IN isolate (A-IN/B-IN) systemically infected all plants, whereas the ES isolate (A-ES/B-ES) failed to do so. Pseudo-recombinant analyses revealed that DNA-B from the IN isolate complemented A-ES in trans, enabling systemic spread, while B-ES accumulated poorly and supported systemic infection only inefficiently. Although both A components replicated locally in tomato, DNA-A from the IN isolate was unable or only marginally able to infect systemically in the absence of DNA-B, demonstrating an essential contribution of DNA-B to long-distance movement. In N. benthamiana, both isolates established systemic infections even as monopartite viruses, though with substantially reduced viral titers and attenuated symptoms, indicating that host factors can partially compensate for the absence of DNA-B. Using a DsRed-tagged {Delta}CP mutant of ToLCNDV-ES, we further show that coat protein is required for systemic movement in N. benthamiana, despite the presence of DNA-B-encoded movement functions. Collectively, these results uncover striking host- and isolate-dependent differences in component compatibility and demonstrate that systemic infection by ToLCNDV-IN DNA-A in tomato requires DNA-B, while ToLCNDV-ES additionally depends on coat protein for efficient movement in N. benthamiana.